Formation Of Diffusion Layer Research Articles

Nanomechanical behaviour of Al-Ti layered composites produced by accumulative roll bonding

In this study Ti-foils were roll bonded together with commercially pure aluminium AA1050. The laminates were produced by using two 1 mm thick AA1050 sheets at the outer side of the stack combined with 100 μm thick Ti-foils as an intermediate layer for each accumulative roll bonding process. The samples were rolled up to 4 ARB cycles. Subsequently the sheets were post-process heat treated at 180°C, 400°C or 600°C, respectively, for 24 hours. The local mechanical behaviour of the Al/Ti intermetallic interfaces have been investigated using nanoindentation experiments. A strong dependence between annealing-temperature, – time and deformation grade is detected. While a heat treatment at 180°C only leads to a weak bonding between Al and Ti with a preservation of the UFG structure, temperatures up to 600°C are causing a complete recrystallisation of the microstructure and formation of diffusion layers with different Al and Ti concentrations.

Formation of Diffusion Layer and Its Influences on Heat Transfer for Coated Tools

A novel structure model of diffusion layer of coated cutting tools is proposed. Equations of effective thermal conductivity for diffusion layer and equivalent layer are derived by using analytical methods of Maxwll-Eucken1 model,Series model and multilayer equivalent model. The value of the effective thermal conductivity of a specific coated cutting tool is calculated by using the new model. Temperature values of cutting tools with and without consideration of the diffusion layer are obtained by using finite element method. Results reveal that the calculated temperature with the new model is more accurate than the conventional one comparing with measured temperature. The new method can help the choice and design of coated tools with more accurate theoretical for manufacturing industries.

Vacuum carburizing of chromium-nickel steel

The main features of formation of diffusion layers due to vacuum carburizing of chromium-nickel steel 20Kh2N4A in an acetylene medium are considered. Analysis of the structure of the saturated surface and of the results of carburizing is used to show that the diffusion layer is formed under a thin layer of condensed carbon in a kinetic regime the intensity of which is determined by the structure of the carbon layer and by the rate of its dissolution.

Magnetic field effects on the initial stages of electrodeposition processes

The initial stages of Cu, Ag and Zn electrodeposition processes are investigated in a magnetic (B) field superimposed perpendicularly to an Au(1 1 1) electrode. Cyclic voltammetry shows no B field effects on the monolayer formation at underpotentials. On the other hand, the nucleation in the overpotential region is clearly inhibited. Since these phenomena are independent of the magnetic susceptibility of the metal species, the present results may be interpreted in terms of B field effects on the surface diffusion of ad-atoms or the 2D diffusion layer formation.

Nanocrystallization kinetics and glass forming ability of theFe65Nb10B25metallic alloy

The crystallization kinetics of glassy ${\mathrm{Fe}}_{65}{\mathrm{Nb}}_{10}{\mathrm{B}}_{25}$ melt-spun ribbons is studied by differential scanning calorimetry in the mode of continuous heating and isothermal annealing and by x-ray diffraction and transmission electron microscopy. Continuous heat treatments of the ribbons show the presence of multiple exothermic peaks before melting. The low-temperature peak corresponds to the precipitation of nanoscale ${\mathrm{Fe}}_{23}{\mathrm{B}}_{6}$-type crystalline metastable phase, and further annealing leads to its transformation into the metastable ${\mathrm{Fe}}_{3}\mathrm{B}$ phase and subsequent formation of $\mathrm{bcc}\text{\ensuremath{-}}\mathrm{Fe}$, ${\mathrm{Fe}}_{2}\mathrm{B}$, and FeNbB stable crystalline phases. The nucleation frequency and the growth rate are determined at selected temperatures from the analysis of the microstructures that emerge during the ${\mathrm{Fe}}_{23}{\mathrm{B}}_{6}$-type nanocrystallization. The master curve method is used to obtain the apparent activation energy and the Avrami exponent at the nanocrystallization onset. The nanocrystallization kinetics is explained in the framework of the Kolmogorov-Johnson-Mehl-Avrami theory. The rejection of insoluble alloy atoms during primary crystallization, the formation of diffusion layers around the crystals, and the decrease in the nucleation frequency caused by alloy enrichment of the residual disordered matrix is modeled through a soft impingement factor. Estimated values for the interfacial energy that provide a satisfactory agreement between experiments and modeling are derived considering that homogeneous nucleation frequency and interface-controlled grain growth are dominant at the onset of the nanocrystallization. Consequently, the time-temperature-transformation diagram is also drawn and the critical cooling rate estimated for this glass forming alloy.

Effect of Fusing Treatment on Fatigue Strength of Thermally Sprayed Steels with Co-Based Self-Fluxing Alloy Coating

Rotational bending fatigue tests were carried out on a medium carbon steel with a thermally sprayed Co-based alloy coating. The effect of two different fusing treatments on the fatigue strength of fused specimens was investigated. Fusing treatment was performed using a vacuum furnace, and an induction heating system. When the specimens were treated in vacuum furnace at 1373 K for 4 h, the diffusion layer providing a strong adhesive force were formed at the interface between the coating and substrate. As a result, fatigue strength remarkably increased in comparison with the uncoated specimens. On the contrary, for the treated specimens with an induction heating system at 1373 K for 120 s, since these specimens had a lower adhesive force due to no formation of diffusion layer, leading to delamination of the entire coating.

Regularities in the formation of diffusion layers in magnesium-aluminum composite

The results of metallographic investigations, micromechanical tests, and X-ray structural analysis of the layered composite of the Al-Mg system are presented. It is found that in the initial state, intermetallic phases are absent in the contact region. Starting from t = 150°C, local regions of the diffusion layers are formed. An increase in the keeping time and temperature leads to growth (towards A1) in the thickness of layers and their hardness, namely, to 2000–3000 MPa on heating to 150°C for 1 h and 4500–5000 MPa at t = 400°C for τ = 12 h. When kept for 16 h at 400°C, the layer preferentially involves the Mg2Al3 phase with the hexagonal lattice.

Microstructure and bond strength of HA(+ ZrO 2 + Y 2O 3)/Ti6Al4V composite coatings fabricated by RF magnetron sputtering

Novel HA(+ ZrO 2 + Y 2O 3)/Ti6Al4V composite coatings have been developed successfully by radio-frequency magnetron sputtering technique (RF-MS). The surface morphology, phase composition and Ca / P ratio analysis of the HA(+ ZrO 2 + Y 2O 3) composite coatings were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). Results showed that the average thickness of HA(+ ZrO 2 + Y 2O 3) composite coatings was in the range of 3∼4 μm. The surface morphology of HA(+ ZrO 2 + Y 2O 3) composite coating was rough and uneven with the well-distributed concaves. The average diameter of these concaves was in the range of 0.5∼2 μm, and the surface area of these concaves was about 30∼40%. The XRD and EDS analysis of the sputtered coatings indicated that the n(Ca) / n(P) ratios in the as-sputtered and post-annealing coatings were both in the range of 1.77∼1.79. The pull-out test results showed that the ultimate bond strength of sputtered HA(+ ZrO 2 + Y 2O 3)/Ti6Al4V composite coatings was 59.6 MPa. Furthermore, the bonding strength of HA(+ ZrO 2 + Y 2O 3)/Ti6Al4V composite coatings was enhanced with the increasing of sputtering power and the addition of YSZ. SEM interface morphology on the cross-section of HA(+ ZrO 2 + Y 2O 3)/Ti6Al4V composite coatings showed that there wasn't any pore or crackle in the coating/substrate interface. The diffusion distribution of elements in interfacial zone indicated that there was a diffusion layer between HA film and Ti–6Al–4V substrate. The thickness of the diffusion layer for different elements was about 1.5 μm∼2.0 μm. The high bond strength of the sputtered HA(+ ZrO 2 + Y 2O 3)/Ti6Al4V composite coatings was attributed to the formation of diffusion layer in interfacial zone, the sputter cleaning and ion bombarding processes, and the mechanical interlocking effect resulting from the rougher surface of Ti–6Al–4V substrate treated by sandblasting and etching.

Kinetics of adsorption of polyvinylamine on cellulose fibers: II. Adsorption from electrolyte solutions

Adsorption from electrolyte solutions of fully hydrolyzed polyvinylamine on cellulose fibers was investigated by supplying the polymer to the fibers at controlled rate. This was implemented by employing a reactor only open to the fluid in which the fiber dispersion were confined and homogenized. The adsorbed layers may be defined as diffuse or dense layers. Diffuse layers are characterized by a surface coverage limited to 0.65 mg/g cellulose in salt-free solutions. Addition of NaCl or CaCl 2 to the fiber dispersion and the polymer solution promotes the adsorption rate and increases the amount of adsorption to 1.5 mg/g cellulose. For dense polymer layers, for which the coverage amounts to values close to 10 mg/g cellulose in salt-free systems, addition of electrolyte does not change the kinetic and adsorption characteristics. Insofar as the variation of the molecular areas of the polymer within the diffuse layers as a function of the ionic strength parallels the variation of the molecular characteristics of solute molecules, the formation of diffuse layers is expected to proceed by random deposition of solute molecules which later individually sustain strong reconformation. Adsorption isotherms show a limited influence of the ionic strength. Obviously, the passage from dense layers of high surface coverage to low adsorption values at equilibrium requires extended reconformation of adsorbed macromolecules and desorption of a great part of the molecules already adsorbed.

Behavior of Diffusion Layer Formation for TiNi/6061Al Smart Composites by Vacum hot Press

2.7vol%TiNi/6061 Al composites with TiNi shape memory alloy as reinforcement were fabricated by vacuum hot press. It was investigated by OM, SEM, EPMA and XRD analysis for the behavior of diffusion layer formation on various heat treatment condition. Thickness of diffusion layer was increased proportionally according to heat treatment time. The layer was formed by the mutual diffusion of TiNi and Al. The diffusion rate from TiNi fiber to Al matrix was faster than that of reverse diffusion path. The more diffused layer was formed in Al matrix. The diffusion at interface layer was consisted of Ti, Ni analyzed by EPMA, XRD results.

Electrolytic plasma processing for cleaning and metal-coating of steel surfaces

Electrolytic plasma processing (EPP) involves electrolysis and electrical discharge phenomena and it is an emerging, environmentally friendly surface engineering technology. Electrolytic-plasma/material surface interactions during processing can be used for cleaning of metal surfaces, formation of diffusion layers and/or deposition of metal, ceramic and composite coatings. The present work was concerned with cleaning and deposition of metal coatings on steel surfaces for corrosion protection. The effects of processing parameters on (i) cleaning steel surfaces (oxides and contamination); and (ii) Zn and Zn–Al coating deposition were investigated. Surface roughness and oxygen content prior to and after cleaning were evaluated by profilometry and energy dispersive X-ray analysis (EDAX), respectively. The structure of the EPP cleaned outer surface layer as it evolves after the electrolytic–plasma interaction was studied by high resolution TEM. Morphology, microstructure, composition, adhesion and density of EPP-deposited Zn and Zn–Al coatings on cleaned surfaces were studied as a function of processing parameters. Corrosion properties of the cleaned and coated steels were evaluated by corrosion potential and potentiodynamic polarization measurements. The results show that EPP can effectively produce clean surfaces and also metal and alloy coatings at high deposition rates, and it has a great potential as a new plasma surface engineering technique.

Direct bonding of silicon wafers with the concurrent formation of diffusion layers

An original technique for Si-Si direct bonding combined with impurity diffusion in a single process is suggested. A dopant (aluminum) source is located at the interface. The high-temperature treatment of the polished wafers in an oxidizing atmosphere results in the diffusion of Al atoms and the formation of a p-n junction in n-silicon. The presence of aluminum is shown to improve the continuity of the interface. Results obtained are explained within a model whereby the initial contact between the hydrophilic silicon surfaces in a water solution of aluminum nitrate Al(NO3)3 serves to increase the bonding area of the wafers at room temperature due to the interaction of Al-OH groups with water molecules adsorbed on the surfaces of the wafers.

Determination of the coefficient of carbon diffusion for calculating nonisothermal regimes of high-temperature ion nitrocarburizing

1. Based on the theoretical concepts that allow for the effect of the temperature in thermocycling on the elastic properties of the crystal lattice of the solid solution we obtained an equation for calculating the coefficient of carbon diffusion and used it in a mathematical model of the process of nonisothermal INC. 2. The calculation was used to develop thermocycling regimes of INC that provide the formation of diffusion layers of a great thickness at a saturation time reduced to 4 h.

Crystallization of Fe-based amorphous alloys

An Fe 73.5Si 15.5B 7Nb 3Cu 1 alloy with a crystalline grain structure is a soft magnetic material since it has good values of permeability while maintaining a saturation magnetization. Thermal annealing of an amorphous melt spun alloy in the temperature range 480–510°C produces a crystalline dispersion of Fe(Si) particles with diameter of the order of 14 nm embedded in a residual amorphous matrix with a higher crystallization temperature. In this work we correlate experimental measurements of grain size and crystallized fraction of an annealed amorphous Fe 73.5Si 15.5B 7Nb 3Cu 1 alloy, obtained, respectively, by X-ray diffraction and differential scanning calorimetry, with the particle size observed by transmission electron microscopy. The structural development is explained by considering the rejection of insoluble alloy atoms during crystallization with the formation of diffusion layers around the crystals. Growth rates are diminished by the accumulation of the slower diffusing atoms at the growing Fe(Si) interfaces; faster diffusing atoms by alloy enrichment of the residual amorphous matrix can cause a decrease in the nucleation frequency.

Examination of carbon diffusion in niobium clad steel composite

The Nb2 C layer formed in the bonding interface of a niobium clad steel composite at 1023 K for 112 h was examined metallographically and analyzed using the electron microprobe technique. The mechanism of Nb2 C phase diffusion layer formation was discussed using Fick’s law assuming that stationary diffusion of carbon was established in niobium/steel diffusion couples.

List of journals scanned

In the present work, wetting behaviour of Ag–Cu eutectic filler on high nitrogen austenitic stainless steel (HNS) and 316L austenitic stainless steel (316L) base metals was firstly studied using a sessile drop method in high vacuum. The Ag–Cu eutectic filler exhibits completely different dynamic wetting process on the surface of HNS and 316L. The equilibrium contact angle of Ag–Cu/HNS system is lower and its wetting time is shorter than that of Ag–Cu/316L system. Subsequently, brazing experiments were carried out for HNS and 316L base metals using the same filler at 840 °C for a holding period of 5–30 min under high vacuum. Microstructural analysis shows that the 316L/316L joints are composed of α-Cu and fine Ag–Cu eutectic. The HNS/HNS joints consist of β-Ag and coarse Ag–Cu eutectic. The optimal shear strength of HNS/HNS joints (290 MPa) is significantly higher than that of 316L/316L joints (175 MPa) because of the formation of diffusion layer. Therefore, HNS has tremendous potential to take the place of the traditional austenitic stainless steels for industry application.

The application of ultrasonic waves to the electrochemical polymerization of thiophene

AbstractThe electrochemical polymerization of thiophene was carried out both in the presence and absence of ultrasonic waves. Without irradiation, the anode potential increased with increasing current density. Polymerization at high potential gave a low polymer yield and produced macroscopically heterogeneous films. Ultrasonic irradiation resulted in an improvement of polymer yield and in a lowering of the anode potential during polymerization. The effects were especially marked when the polymerizations were carried out at low temperature, low monomer concentration, and high current density. These results are explained by the formation of diffusion layer in the vicinity of the electrode during electrochemical reactions.

含Ｓｉ軸受用アルミニウム青銅とオーステナイト系ステンレス鋼の固相接合 ＩＩ 拡散層の形成と接合強度

含Ｓｉ軸受用アルミニウム青銅とオーステナイト系ステンレス鋼の固相接合 ＩＩ 拡散層の形成と接合強度

焼結鋼におけるモリブデンの拡散合金化過程 Ｉ 鉄‐モリブデン‐炭素系圧粉体拡散対における合金化過程

In order to reveal the diffusion processes of molybdenum in sintered steels, diffusion couples prepared from powder mixture compacts were heated in vacuum at 1523K for 3.6ks, and the diffusion zones were examined mainly by means of EPMA.Carbon in the iron-molybdenum diffusion couples intensively affected the diffusion layer formation through the carbide layers formation. In the diffusion couples containing carbon, the molybdenum diffusion in iron was considerably enhanced by using Mo2, C powder compacts as the coupling partner for iron powder compact or iron-carbon powder mixture compact, as compared with the use of molybdenum and graphite powder mixture compacts of the same composition. The difference in the degree of molybdenum diffusion was attributed to the iron-molybdenum-carbon ternary liquid phase formation in the interface of diffusion couple, as well as the diffusion in the solid phase.

Reactions of chromium diboride with carbon steels under glow-discharge conditions. Part II

A study was made of the zones of diffusional reaction of chromium diboride with carbon steels, cast iron, and Armco iron, forming under glow-discharge conditions. An attempt was made to discover the laws governing the formation of diffusion layers in these systems. It was established that with rise in carbon concentration in the steel the width of the diffusional reaction zone grows, attaining a maximum for a steel with a carbon content of 0.8%. At a carbon concentration in the steel of 1.6% or more, the width of the diffusion zone sharply decreases. In a CrB2-steel system a strong inhibiting influence on diffusion is exerted by the higher chromium carbide Cr3C2.